Desert pavement

A desert pavement, also called reg (in the western Sahara), serir (eastern Sahara), gibber (in Australia), or saï (central Asia) is a desert surface covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size. They typically top alluvial fans. Desert varnish collects on the exposed surface rocks over time.

Scholars debate the mechanics of pavement formation and their age.

https://en.wikipedia.org/wiki/Desert_pavement